DESCRIPTION: (Applicant's abstract) This is a revised proposal for a renewal of project NS29514 on the characterization of the phosphoinositide linked dopamine (DA) receptor. Evidence obtained under this grant supports the existence of the brain DA receptor subtype which is linked to the phosphoinositide second messenger pathway. The receptor appears to be a D1/5 like DA receptor, differing from the classically defined dopamine receptor by coupling to phospholipase C via Gq protein. This potentially novel receptor may mediate some of the physiological and pharmacological effects of DA which cannot be accounted for by the adenylyl cyclase-linked DA receptors. Consequently, the understanding of the actions of DA that are mediated via this receptor has potential implications for therapeutics and diagnosis of various DA-associated neuropathologies, including schizophrenia, Parkinsonism, Huntington's chorea and tardive dyskinesia. Characterizing the functional significance of this receptor protein will depend, to a large extent, on the successful cloning of the cDNA which encodes it. The applicant s preliminary efforts to this end resulted in the identification of a cell line which exclusively expresses the principal investigator-linked DA receptor. Obtaining this cell line facilitated the cloning of this unique DNA fragment which contains elements that are highly conserved among all G-protein coupled receptors. A series of experiments are proposed with the following specific aims: (a) to continue and define the components which transduce signals initiated by this receptor in brain tissue, (b) to isolate the full length DNA which encodes this receptor by screening a DNA library constructed from a human cDNA or from the selected cell line, and determine its nucleotide sequence, and restriction map; c) determine the tissue distribution and relative abundance of the novel receptor message in rat brain, and (d) identify its ligand binding and G-protein coupling domains by expressing and analyzing the characteristics of mutant variants of the receptor. The results of this project will lay a solid foundation for the greater understanding of the role of DA in CNS function and dysfunction, and for evaluating and possibly redefining various models of DA-associated neuropathologies.